The amount of whole blood which must be collected into a commercially prepared collection bag containing the usual amount of anticoagulant is 450 ml. Units inadvertently collected in amounts less than this must be discarded. The purpose of this study is to investigate whether blood collected in a volume of 275 ml will have adequate survival when transfused. Blood will be intentionally undercollected, made into packed red cells, and stored in CPDA-1 anticoagulant the maximum time of 35 days. A small amount of red blood cells will then be labeled with 51Chromium and retransfused into the donor to determine the post-transfusion red cell survival. The post-transfusion survival of red cells inadvertently undercollected because of technical difficulties or donor reactions will also be investigated in this manner.